Temperature stabilized monstable multivibrator

ABSTRACT

A modification to a conventional monostable multivibrator circuit is disclosed for minimizing variations in the width of output pulses produced by the circuit, in particular, pulse width variations resulting from changes in parameters of the transistors resulting from temperature variations. Stabilization is achieved by utilizing an additional transistor as a leg of a voltage divider for supplying bias voltage to the transistors of the multivibrator. When the additional transistor has a temperature response similar to that of the multivibrator transistor, a circuit can be constructed that compensates for changes in parameters of the multivibrator transistors by changing their bias voltage. Two embodiments of the instant invention are disclosed. One utilizes a third transistor that is identical in type to the transistor of the multivibrator while the other uses a transistor of complementary symmetry.

United States Patent [72] Inventor FrancisE.M0rris 3436 Elliott St., San Diego, (Ialii. 92106 [21] Appl.No. 727,448 [22] Filed May8, 1968 [45] Patented Apr. 6, 19711 [54] TEMPERATURE STABILIZED MONSTABLE MULTIVIBRATOR 5 Claims, 3 Drawing Figs.

[52] U.S.Cl 307/273, 328/207,33l/ll3,331/176 [51] Int.Cl H03k3/26 [50] FieldofSearch 307/273, 293; 328/207; 331/1 13, 176

[56] References Cited UNITED STATES PATENTS 2,975,300 3/1961 Havgenetal. 307/273X 2,976,432 3/1961 GeckleJr. 307/273 3,214,602 10/1965 Heyningetal 307/273X 3,239,778 3/1966 Rywak 331/176X 3,264,579 8/1966 Marcus 33l/176X 3,356,863 12/1967 Beck 3,388,344 6/1968 West TRACT: A modification to a conventional monostable multivibrator circuit is disclosed for minimizing variations in the width of output pulses produced by the circuit, in particular, pulse width variations resulting from changes in parameters of the transistors resulting from temperature variations. Stabilization is achieved by utilizing an additional transistor as a leg of a voltage divider for supplying bias voltage to the transistors of the multivibrator. When the additional transistor has a temperature response similar to that of the multivibrator transistor, a circuit can be constructed that compensates for changes in parameters of the multivibrator transistors by changing their bias voltage. Two embodiments of the instant invention are disclosed. One utilizes a third transistor that is identical in type to the transistor of the multivibrator while the other uses a transistor of complementary symmetry.

TEMPERATURE STABILIZED MONSTAIIIJE IVIIJIJIIIVIIIIIATOII STATEMENT OF GOVERNMENT INTEREST The invention described may be manufactured and used by or for the Government of the US. of America for govemmcntal purposes without the payment of any royalties thereon or therefore.

BACKGROUND OF THE INVENTION This invention relates to an improvement for transistorized multivibrators and more particularly to an improved technique and apparatus for stabilizing the output of such multivibrators with changing temperature.

Monostable multivibrators find extensive utility in present electronics arts. Various modifications of the basic monostable multivibrator have been developed, one such modification being the so-cailed voltage variable monostable multivibrator. This type of circuit is arranged to produce an output pulse of fixed duration in response to an input trigger signal. The voltage variable feature relates to the fact that by controlling the biasing voltage to the device, the width of the output pulse may readily be varied.

in applications where the precise width of the output pulse is of great importance, temperature instability of the transistors used in the circuit results in the creation of a problem to which the instant invention is directed. In particular, changes in junction voltage and the forward current transfer ratio (h resulting from temperature change cause concomitant changes in pulse width when the bias voltage is maintained at a constant level. The development of silicone transistors has helped the situation considerably; however, substantial pulse width variations due to temperature variations are still present in state of the an multivibrator.

Various methods have been proposed in the prior art to solve the temperature problem. Most of such methods generally comprise the addition of a sensistor-type resistor or handwound wire resistor having a temperature coefficient to counteract the coefficient of the junction voltage changes. These methods have serious limitations, since they require individual matching due to the broad tolerances in the individual units. It is also difficult to maintain the transistor and resistor at the same temperature.

SUMMARY OF THE INVENTION An object of this invention is to improve the temperature stability of voltage controlled monostable multivibrators.

A more particular object of this invention is to stabilize the output pulse width of a transistorized monostable multivibrator by compensating for changes in the transistor junction voltage resulting from changes in temperature.

The instant invention achieves the above-noted objects by providing an improved technique and apparatus for compensating for transistor junction voltage changes. Essentially, the invention comprises a voltage divider including a constant re sistance and a variable resistance. The midpoint between the two resistances is connected to the base element of a first stage transistor of the multivibrator. The divider is connected across the source of bias voltage and hence the actual bias voltage applied to the first stage is dependent on the value of the divider resistances.

In the preferred embodiment the variable resistance comprises the forward path through a transistor. When the transistor is chosen to have parameters similar to those of the multivibrator first stage, the junction voltage changes in that first stage can be compensated for by opposite changes in the added stage. The bias voltage, therefore, of the first stage is changed in proportion to changes in the junction voltage due to changes in temperature.

The above objects and features of the invention will be better understood from the following detailed description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a schematic diagram of the prior art voltage variable monostable multivibrator;

FIG. 2 is a schematic diagram of one embodiment of the instant invention using complementary transistors; and

FIG. 3 is another embodiment of the instant invention utilizing identical transistors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before considering in detail the improvements to which the instant invention relates, the well-known prior art monostable multivibrator should be discussed briefly. FIG. I illustrates in schematic form the well-known, classical voltage controlled monostable multivibrator. As may be noted, the circuit comprises transistors II and I2 each having base, emitter, and collector elements I3, l I, I5 and Id, I7, and I8, respectively Resistances I9 through 24! establish the operating parameter of the circuit and provide various elements with their proper operating voltages from terminal 25. The details of the noted circuit elements need not be described at this time since they are well known and fully described in the prior art.

It is sufficient to generally note at this time that normally the circuit operates so that transistor II is in its open" or off" condition, while transistor I2 is forward biased and hence in its on condition. When a trigger signal is received at input terminal 26, base I3 of transistor II is driven positive with the result that the transistor II turns on with a rapid voltage drop occurring at collector terminal I5. This rapid voltage drop is transmitted through capacitor 27 to the base I6 of transistor I2. The latter is driven to cutoff and therefore assumes its off condition. Transistor I2 remains off for a period determined by the time constant established by resistances 23 and M and capacitance 2'7, on the one hand, and the voltage at collector IS, on the other. Both factors are determinative of the width of final output pulses appearing at output terminal 28. The voltage at collector I5 is determined by the collector and consequently by the base-to-emitter voltage. The base emitter junction voltage varies with changes in temperature in all available state of the art transistors and, as noted previously, is the primary cause of temperature instability in the classical circuit. This is true, since with the changing junction voltage, the effective voltage at base I3 is changed, and hence the current flow through the transistor and the collector voltage are thereby modified.

It should be noted at this point that in the other FIGS., to wit, FIG. 2 and FIG. 3, the identical reference numerals have been utilized where identical components are shown. Not all the components of these latter two schematic circuit diagrams have been numbered since they are intended really to illustrate the additional components that the instant invention compnses.

Referring then to FIG. 2, one embodiment of the improvement of this invention is illustrated. The improvement comprises the transistor 29, having a base: 39, a collector 3I, and an emitter 32 connected in circuit with a resistance 33. Transistor 29 may be thought of as a variable resistance and hence the combination of the transistor and resistor 33 to form a voltage divider in the sense that the resistor 33 and the transistor 29 are connected in series between the applied potential and ground. The base I3 of transistor II is connected to emitter 32 of transistor 29 and hence to the midpoint of the voltage divider comprising the transistor 29 and the 33 resistance.

Component values are chosen for the circuit such that the voltage at emitter 32 will vary in an opposite manner to the junction voltage change in transistor II with changes in temperature and hence the two variations will cancel each other out and the transistor II will be compensated. The latter occurs by reason of the fact that the control voltage for the overall voltage control device is varied by resistor 2d and hence by the voltage at base 30 of transistor 29. Between base 30 and emitter 32, a base emitter junction occurs that will be subject to the same junction voltage vs. temperature change characteristic as transistor 11. By reason of the complementary symmetry arrangement of FIG. 2, i.e., transistor 11 is a NPN type and transistor 29 is a PNP type, direct coupling of base 13 to emitter 32 achieves the proper compensating condition. The overall operation, then, results in the voltage at base 13 being automatically adjusted to compensate for any base emitter junction voltage changes in transistor 11 resulting from variations in temperature.

As indicated previously, the operation of transistor 29 may also be thought of as a variable resistance since for a voltage change to occur at emitter 32, the effective resistance from that point to ground obviously must vary.

It is imperative in the embodiment of FIG. 2, and in that of FIG. 3 as well, that the transistors be chosen to have matching temperature change characteristics and furthermore in the actual circuit embodiment they be subjected to the same temperature changes. The latter condition will normally be met if the two transistors are mounted on a common heat sink.

Referring now to FIG. 3, another embodiment of the invention is illustrated. The embodiment of FIG. 3 differs from that of FIG. 2 only by reason of the fact that it does not utilize the complementary transistor technique, but instead comprises a second transistor identical to the multivibrator stage transistor, the second transistor being employed as the compensating device. Referring then to FIG. 3, it can be noted that transistor 34, the compensating stage, is of the same type as transistor 11. Transistor 34 comprises base, emitter, and collector elements 35, 36, and 37, respectively. The voltage divider comprising resistances 38 and 39, collector load resistance 40, and emitter resistance 41 comprise the additional components, compared to the classical circuit, required for this embodiment of the invention.

The function of the FIG. 3 embodiment is identical to that of FIG. 2 in that the net operative result of both is to vary the voltage on base 13 in accordance with junction voltage changes in the transistor 11. In the FIG. 3 embodiment, because similar type transistors are utilized, the collector 37 of transistor 34 is directly connected to the base 13 of transistor 11. As the base emitter junction voltage of transistor 34 changes with temperature, it follows that the collector 37 voltage and hence, base 13 voltage of transistor 11 will also change in a related manner.

For optimum operation of the FIG. 3 device, it should be reemphasized that transistor II and transistor 34 should be very closely matched with regard to their operating characteristics.

It should be noted at this point that throughout the specification and claims, reference has been made to portions of the circuit as stages. In that regard, transistor 11 has been referred to as the first transistor stage, transistor 12 as the second transistor stage, and the compensating transistor 29 or 34 as the third transistor stage.

By utilizing either of the embodiments of the invention as disclosed, voltage controlled monostable multivibrators have been constructed by the inventor that exhibit temperature stability heretofore unattainable. It is therefore apparent that with the minimum components required by the teachings of this invention, the operation of the classical monostable multivibrator may be modified and greatly enhanced.

Although the invention has been particularly described with reference to two embodiments thereof, it should be understood that it need not be limited thereto, for various changes and modifications could be made by one having ordinary skill in the art without departing from the spirit and scope of the invention as defined in the following claims.

I claim:

1. In a solid-state voltage-variable monostable multivibrator circuit of the type comprising:

first and second transistor stages responsive to a bias voltage zfipplied to said first stage for normally maintaining said rrst stage in a OFF" condition and said second stage in an ON" condition;

said first stage being responsive to input trigger pulses of a predetermined polarity such that said first stage is caused to turn ON" by receipt of one of such pulses; means for coupling said first stage to said second stage so that turning said first stage ON" causes said second stage to turn OFF for a predetermined time period;

said time period being a determinable function of the bias voltage applied to said first stage transistor;

the improvement comprising means for stabilizing said time period and comprising; a voltage divider comprising a constant resistance and the variable resistance developed between the emitter and collector of a third transistor serially connected with a source of voltage, said third transistor being arranged to accept pulses as an input to its base, and the series connection between said constant resistance and said third transistor being connected to provide the base of said first stage transistor with biasing voltage, and with input trigger pulses; and

said third transistor being selected to vary its resistance in response to temperature changes and in a manner related to the change in parameters of said first stage transistor with temperature, whereby to provide a biasing voltage as a function of temperature and stabilize said time period.

2. The circuit of claim 1 wherein said third transistor is of complementary symmetry to said first transistor stage.

3. The circuit of claim 2 wherein said first stage includes an NPN transistor having base, emitter and collector elements and said third stage includes a PNP transistor having base, emitter and collector elements, and

said base of said NPN transistor being connected to said emitter of said PNP transistor.

4 The circuit of claim I wherein said third transistor has the same characteristics and is of the same type as said first transistor.

5. The circuit of claim 4 wherein said first and third transistors are of the NPN type and each includes base, emitter and collector elements; and

said first transistors base being connected to said third transistors collector. 

1. In a solid-state voltage-variable monostable multivibrator circuit of the type comprising: first and second transistor stages responsive to a bias voltage applied to said first stage for normally maintaining said first stage in a ''''OFF'''' condition and said second stage in an ''''ON'''' condition; said first stage being responsive to input trigger pulses of a predetermined polarity such that said first stage is caused to turn ''''ON'''' by receipt of one of such pulses; means for coupling said first stage to said second stage so that turning said first stage ''''ON'''' causes said second stage to turn ''''OFF'''' for a predetermined time period; said time period being a determinable function of the bias voltage applied to said first stage transistor; the improvement comprising means for stabilizing said time period and comprising; a voltage divider comprising a constant resistance and the variable resistance developed between the emitter and collector of a third transistor serially connected with a source of voltage, said third transistor being arranged to accept pulses as an input to its base, and the series connection between said constant resistance and said third transistor being connected to provide the base of said first stage transistor with biasing voltage, and with input trigger pulses; and said third transistor being selected to vary its resistance in response to temperature changes and in a manner related to the change in parameters of said first stage transistor with temperature, whereby to provide a biasing voltage as a function of temperature and stabilize said time period.
 2. The circuit of claim 1 wherein said third transistor is of complementary symmetry to said first transistor stage.
 3. The circuit of claim 2 wherein said first stage includes an NPN transistor having base, emitter and collector elements and said third stage includes a PNP transistor having base, emitter and collector elements, and said base of said NPN transistor being connected to said emitter of said PNP transistor. 4 The circuit of claim 1 wherein said third transistor has the same characteristics and is of the same type as said first transistor.
 5. The circuit of claim 4 wherein said first and third transistors are of the NPN type and each includes base, emitter and collector elements; and said first transistor''s base being connected to said third transistor''s collector. 